The pair backed the Samsung Hope Relay, in which participants create an animated avatar on a mobile app and track their total distances using GPS.

Users could have their avatars displayed on the side of the Olympic Torch Relay coach during its tour around Britain, or on Samsung advertising billboards.

‘It’s a nice, obvious contribution from the public,’ Pendleton said. ‘You don’t have to do much, we’re not asking you to donate your money, we’re just asking you to donate your legs for a little bit.’

Children’s charities – including London-based Kids Company, International Inspiration and a cause decided by Games bosses – will be the main beneficiaries. The initiative could expand to 20 countries.

Meanwhile, reigning Olympic champion Pendleton admitted she was affected by criticism from fellow rider Mark Cavendish she has committed too much time to advertising rather than training.

Speaking at the Hope Relay launch at London’s City Hall, which included a video message from David Beckham, the 31-year-old added: ‘It’s been difficult at times but I’ve been very picky with what I’ve been involved in. I could’ve done a lot more but chose not to.’

The Hope Relay app can be downloaded from the Google Play store, Apple app store or by texting 61116 and following the link. It runs until August 12.